Surface mount technology has made it possible to densely populate both sides of a circuit board with semiconductor devices. Because leads of a surface mount integrated circuit (IC) package may be placed closer together than through-hole pins of a dual-in-line package (DIP), the component size of surface mount ICs has correspondingly decreased. These small packages have been termed small-outline IC packages and chip carriers. Chip carriers are typically used in applications that require large lead counts and employ a variety of mounting techniques such as, flat packs, quad flat packs (QFP), J-leads, Gull-wing leads, leadless, and the more recent development of ball grid arrays (BGAs).
The ball grid array mounting technique uses rows and columns of closely positioned solder balls located on one side of the package as the outer leads of the integrated circuit. Ball grid array packages offer many advantages including lower yield loss from bent leads and misregistration, higher throughput from greater placement tolerances and a more repeatable assembly process. However, a major concern with the ball grid array package is non-uniformity of the solder balls which may translate to defective solder joints. It is of extreme importance, therefore, to inspect and verify the physical parameters of each ball in the ball grid array to insure that the parameters fall within manufacturing specifications. However, because the solder balls are arranged in rows and columns, the profiles of the solder balls located behind the outer rows and columns are not easily inspected.
The importance of visual mechanical inspection for BGA devices is well appreciated in the art. Various inspection systems and apparatus are currently used in the manufacturing industry, such as , for example, those found and described in U.S. Pat. Nos. 5,162,866; 5,212,390; 5,450,206; 5,465,152; 5,652,658; and 5,621,530. However, conventional lead inspection techniques suffer from a variety of drawbacks relating to size constraints, power consumption, cost, and reliability of the inspection system. For example, some lead inspection systems employ an optical beam which scans across the grid array to verify the physical parameters of each connector in the array. The use of moving parts in such systems, however, increases size requirements of the inspecting device, and reduces reliability.
What is desired is a lead inspection system which can reliably inspect the pertinent parameters of a grid array package. It is also desirable to provide a lead inspection apparatus which is simple in design, and space efficient. It is an object of the present invention, therefore, to provide a lead inspection system which is space efficient and simple in design, and which can be constructed into a compact inspection module for in-process application. It is yet another object of the present invention to provide a lead inspection apparatus which attains a high inspection speed. It is a further object of the present invention to provide a lead inspection system which reliably inspects the pertinent parameters of a grid array and which minimizes the use of moving parts.
These and additional objects are accomplished by the various aspects of the present invention wherein, briefly, according to a principal aspect, an inspection technique is provided which makes use of machine vision in conjunction with a customized optical system to capture different oblique images of the grid array. The captured images are analyzed and used for computation of the pertinent parameters required for inspection analysis.
Accordingly, a first aspect of the present invention is directed to an inspection apparatus for an electronic package having a grid array of connectors mounted on a substrate. The inspection apparatus includes an image capturing device and an image providing means for providing a plurality of images of the grid array to the image capturing device, wherein each of the plurality of images corresponds to a different perspective view of the grid array. Furthermore, each of the plurality of images which are captured by the image capturing device are mappable to a single coordinate system. By using a single coordinate system to compare the relative locations of solder balls in each of the captured images, the spatial coordinates and physical parameters of each solder ball may be calculated.
A second aspect of the present invention is directed to an inspection apparatus for an electronic package having a grid array of connectors mounted on a substrate. The apparatus comprises an image capturing device; a beam splitter; and at least two image reflecting devices, positioned on either side of the beam splitter for directing a first oblique image and a second oblique image of the grid array to the image capturing device. More specifically, a first reflecting device directs a first image of the grid array to the beam splitter, the first image corresponding to a first perspective view of the grid array. A second reflecting device directs a second image of the grid array to the beam splitter, the second image corresponding to a second perspective view of the grid array which is different from that of the first perspective view. The image capturing device captures the first and second oblique image from the beam splitter. The first and second captured images are directly mappable to a single coordinate system, and are used by the apparatus to compute the spatial coordinates and physical parameters of each solder ball in the grid array.
A third aspect of the present invention is directed to an inspection apparatus for an electronic package having a grid array of connectors mounted on a substrate. The apparatus comprises a plurality of image capturing devices, including a first image capturing device an a second image capturing device. The first image capturing device is positioned to capture a first oblique image of the grid array form a first perspective, and the second image capturing device is positioned to capture a second oblique image of the grid array from a second perspective which is different than that of the first perspective. The apparatus further includes converting means for converting the first image and second image to respective images which are both mappable to a single coordinate system. The apparatus further includes calculating means adapted to receive each of the converted images from the converting means for using at least two of a plurality of captured images to calculate the spatial coordinate values of each connector of the grid array.
A fourth aspect of the present invention is directed to a method for computing spatial coordinate values of each connector in the grid array of an electronic package. The method comprises the steps of providing to an image capturing device a first oblique image of the grid array and a second oblique image of the grid array; assigning to the first and second image a common X, Y coordinate system for describing relative positions of image points within each respective first and second image. The method further includes the step of using the X, Y coordinate values of the respective first and second image points to compute representative spatial coordinates X, Y, Z of each connector of the grid array.
A fifth aspect of the present invention is directed to a method for inspecting an array of external lead connectors mounted on a substrate of an electronic package. The method comprises these steps of providing a plurality of images of the grid array to an image capturing device, wherein each of the plurality of images corresponds to a different perspective view of the grid array, and wherein each of the plurality of images is mappable to a single coordinate system; using at least two of the plurality of captured images to calculate spatial coordinate values of each connector of the grid array; and comparing the calculating spatial coordinate values with predetermined values to determine whether the electronic package meets acceptable manufacturing standards.
A sixth aspect of the present invention is directed to a method for inspecting an array of external lead connectors mounted on a substrate of an electronic package. The method comprises the steps of providing to an image capturing device a first oblique image of the grid array and a second oblique image of the grid array; mapping the first and second images to a X, Y coordinate system; using X, Y coordinate values of image points within the first and second images to compute representative spatial coordinates (X, Y, Z) of each connector of the grid array; and comparing the computed spatial coordinate values with predetermined values to determine whether the electronic package meets acceptable manufacturing standards.
By using the technique of the present invention, lead inspection of electronic packages may be performed without moving parts, thereby increasing the reliability of the inspection technique. Furthermore, the inspection system of the present invention is able to be constructed into a compact inspection module for in-process applications, and requires less space than that of conventional inspection systems. Additionally, the inspection system of the present invention is simple in design and is less costly than many conventional lead inspection systems.
Additional objects, features and advantages of the various aspects of the present invention will become apparent from the following description of its preferred embodiments, which description should be taken in conjunction with the accompanying drawings.